The present invention relates to an exposure device forming latent images by exposing members to be scanned (also referred to as “image carriers”, provided in image forming portions that perform an electrophotographic image formation process to a light beam, such as a laser beam, modulated in accordance with image data. The present invention also relates to an image forming apparatus provided with such an exposure device.
Conventionally, image forming apparatuses such as copiers or printers are provided with an exposure device forming a static latent image by scanning an image carrier with a modulated light beam such as a laser beam. A light beam such as a laser beam is modulated based on image data of a read document or image data sent over, for example, a network. Image forming apparatuses perform image formation by transferring a developing agent image (hereinafter, referred to as “toner image”) obtained by developing this static latent image via an intermediate transfer belt onto a recording medium.
Generally, such image forming apparatuses often use a laser beam exposure device as described above in which the modulation speed of the light beam is high, and thus the scanning speed is also high.
On the other hand, color image forming apparatuses that are capable of color image formation have become widespread recently, and thus there is a demand, for example, for higher image forming speeds, for smaller apparatuses, and for consistent image quality in image formation on various recording media (hereinafter, referred to as “paper”) such as thick paper, thin paper or recycled paper.
For this reason, recent color image forming apparatuses are provided with a plurality of image forming portions performing an electrophotographic image formation process with different colors, and use a tandem structure for the intermediate transfer system in which color toner images formed on image carriers provided in the image forming portions are temporarily transferred to an intermediate transfer belt and then transferred to paper.
Thus, the only object on which color toner images are overlapped is the transfer belt, and thus stable image formation can be performed that is not affected by the paper type.
Furthermore, in such color image forming apparatuses using a tandem structure for the intermediate transfer system, an exposure device is provided below the image forming portions in view of, for example, downsizing and usability of the apparatus. The exposure device irradiates a light beam through optical transmission members (irradiation windows) made of glass or the like formed in a housing to image carriers above the exposure device.
However, when the exposure device is provided below the image forming portions, particle dust such as toner may drop from the image forming portions, so that the optical transmission members of the exposure device become dirty, and image writing defects may be caused. Particle dust such as toner tends to drop, for example, when a developing device performing development is operating during an image formation operation, or even outside image formation operation, when the developing device is exchanged.
For this reason, as is disclosed in JP 2002-148910A, a color image forming apparatus has been recently proposed that is provided with a shutter member opposing optical transmission members (seal glass) through which a light beam is irradiated so that the shutter member shuts the optical transmission members through which a light beam is irradiated at times in which no image formation operation is performed. Furthermore, in this color image forming apparatus, an airflow is formed in the vicinity of a light path of the light beam during image formation, so that the optical transmission members are prevented from becoming dirty with toner.
However, even when the optical transmission members are simply shut by the shutter member, there is a possibility that particle dust such as toner is accumulated on the shutter member or around the shutter member, for example, while the developing device is exchanged or while the apparatus is not used and on stand-by, and the accumulated particle dust, such as toner, may drop while the shutter member is operated to open the optical transmission members, so that the optical transmission members become dirty.
It is an object of the present invention to provide an exposure device with which particle dust, such as toner, accumulated on a shutter member or around the shutter member while the shutter member shuts optical transmission members can be prevented from adhering to the optical transmission members while the shutter member is operating. It is also an object of the present invention to provide an image forming apparatus provided with such an exposures device.